Investigations are being conducted on the teratogenicity of heavy metals found in the environment. Metals already found to be teratogenic are investigated to determine site and mode of action and possible interaction with other heavy metals. Special emphasis is being placed on the problem of permeability of the placenta and embryonic membranes. Radioactive isotopes of heavy metals and radioautography are being used to investigate passage of teratogen across the placenta and its site of localization. The fine structure of the early placenta is being studied to correlate structure with placental transport of teratogens. Electron microscopy is also being done on early embryos to try to find early changes caused by heavy metal teratogens. Since heavy metals are known to inhibit enzyme activity, the possible teratogenic role of enzyme inhibition is being studied. Metals under particular scrutiny are lead, cadmium, chromium and mercury. Other metals are also being studied.